acoggan said:
Inadequate filling time. (Note that I'm ignoring your strawman assertion that it must be the heart, and not the cardiovascular system, that is the limiting factor.)
That, my friend, in not a mechanism. Besides, in general, HR doesn't change much at VO2 max hence filling time should not change to explain the drop in output.
Because the heart isn't ischemic, it's just been pushed to/beyond it's maximal pumping capacity.
BTW, Frank, next Thursday I'm going to be explaining this (and other) factors influencing VO2max to my cardiologist colleagues here at Wash U (one of the top 10 medical schools in world, BTW)...perhaps you'd like to pop by and pick up a few CEU yourself? (Oh wait, that's right: you aren't a licensed physician, and in fact haven't been one in years.)
LOL. Filling time decreases as HR increases at all heart rates. What "pushes" the heart beyond its maximum pumping capacity? Why does the "maximum pumping capacity" of the heart depend upon how it is measured (running, cycling, rowing, etc)? When you explain it to the real experts in cardiac physiology, the cardiac anesthesiologists, let me know. It would be worth a chuckle or two to be there. Ask them what they think of your filling time "mechanism" to explain the drop at VO2 max. I doubt the cardiologists will buy your explanation either because there is no data to support what you say. But, as I said before, ignorance is bliss.
BTW, did you know I was a teaching perfessor at UCSF Medical School, Dept of Anesthesiology, considered by many to be the top anesthesiology department in the nation, when I retired from medicine? But, perhaps I forgot everything I knew or since then the knowledge that was known then all got turned on its head.
Anyhow, I am still looking forward to hearing about your mechanism to explain this phenomenon. Feel free to invoke the entire CV system if you wish (although I wouldn't consider the entire CV system as "central" and it won't help anyhow).